Baslle-Doelsch,I., Meunier,J.D. and Parron,C.(2005): Another continental pool in the terrestrial silicon cycle. Nature, 433, 399-402.

『陸域ケイ素循環におけるもう一つの陸のプール』

『（Abstract）
　Silicon is the second most abundant element on Earth. It is an important nutrient for phytoplankton and is readily absorbed by terrestrial vegetation; it also assists the removal of carbon dioxide from the atmosphere through the weathering of silicates. But the continental cycle of silicon is not well known, and only a few studies have attempted to use silicon stable isotopes (28Si, 29Si and 30Si) to quantify the continental silicon reservoirs. Dissolved silicon in sea and river waters forms a reservoir of mean isotopic value +1.1‰ (refs 7, 10). It is enriched in 30Si with respect to the igneous rocks reservoir, which has a mean isotopic value of -0.3‰ (refs 4, 9). This enrichment can only be produced by a major fractionation during weathering, and should result in the formation of a continental 30Si-depleted reservoir. Such a reservoir, however, has not been identified to date. Here we analyse silicon isotopes of in situ quartz from a sandstone series in France, using a new-generation secondary ion mass spectrometry apparatus. We show that quartz that precipitates as siliceous cements forms a strongly 30Si-depleted reservoir with isotopic values down to -5.7‰, a more negative value than any previously published for terrestrial samples. Our findings suggest that quartz re-precipitation plays an important role in the biogeochemical cycle of silicon.』

『（要旨）
　ケイ素は地球で２番目に多い元素である。それは植物プランクトンにとって重要な栄養分であり、陸上植物により容易に吸収される；また珪酸塩の風化をとおして大気からの二酸化炭素の除去を促進している。しかしケイ素の大陸での循環は十分には分かっておらず、大陸のケイ素リザーバを定量化するためのケイ素安定同位体（28Si、29Si、30Si）を使用した研究はほんわずかしか試みられていない。海水と河川水中の溶存ケイ素は平均同位体値＋1.1‰（refs 7, 10）をもつリザーバを形成している。火成岩リザーバでは30Siに富み、平均同位体値は−0.3‰（refs 4, 9）である。この濃縮は風化中の主要な分別作用によってのみもたらせれ、30Siが減損した大陸リザーバを形成するに違いない。しかし、そのようなリザーバは今まで確認されていない。ここで我々は、フランスの砂岩系統からの現位置の石英について、新世代型二次イオン質量分析装置を用いて、ケイ素同位体の分析を行っている。ケイ質セメント（膠結物）として沈殿する石英は、陸上試料について従来報告されたどれよりも大きな負の値である−5.7‰という同位体値をもつ、強く30Siに減損したリザーバを形成することを、我々は示している。我々の発見は、石英の再沈殿はケイ素の生物地球化学循環で大事な役割を果たすことを示している。』

(Text)
Methods
　Mean river water isotopic value
　Notation of isotopic data
　SIMS measurements
(References)
Acknowledgements

陸域環境におけるケイ素の生物地球化学循環（参考文献24から作成）。D、溶解；P、沈殿；T、輸送；E、後成；Up、取込み；De、死。δ30Siの範囲は以下からとられている：内因的岩石（4と本研究）；土壌溶液；植物オパール；新生粘土；土壌および地下水でのケイ（珪酸）化作用（本研究）；地下水（本研究と13）；河川水；浮遊粒状物質。矢印につけられた数字はTモル（1012モル／年）単位のフラックスを示す（29と30）。

〔Baslle-Doelsch,I., Meunier,J.D. and Parron,C.(2005): Another continental pool in the terrestrial silicon cycle. Nature, 433, 399-402.の401pから〕

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